1. Field of the Invention
The invention is directed to a battery composed of at least two fuel cells that respectively comprise a negative pole plate, a membrane electrode unit and a positive pole plate that are connected to one another in a mechanically rigidly, gas-tight and electronically insulating manner by a frame element.
2. Description of the Related Art
Up to now, such batteries wherein every fuel cell of the battery respectively has a negative and a positive pole plate are disclosed, for example, by German Letters Patent 44 42 285; however, the problem of liquid cooling of such fuel batteries has not yet been solved. A liquid coolant is desirable for stationary applications wherein the waste heat is to be utilized in order to keep the required heat exchanger and the distribution of the heat compact.
Liquid-cooled fuel cell batteries are known that, however, respectively contain only individual contact or pole plates at the positive and at the negative end of the battery. Within the battery, these individual contact or pole plates are replaced by what are referred to as bipolar plates, which are often fashioned hollow. The liquid coolant of the known liquid-cooled batteries is located in the cavities of the bipolar plates. Previously known bipolar plates adjoin, on the one hand, the anode space and, on the other hand, the cathode space of the individual fuel cells to be connected to one another. When a traditional battery is assembled, the bipolar plates are stacked on top of one another with the membrane electrode units of the individual fuel cells and are mechanically joined to one another by screw bolts, tie rods or other clamp devices. A single pole or contact plate is then respectively located at the end. This system is also referred to as filter press technique (see, for example, W. Vielstich from "Brennstoffelemente", Verlag Chemie GmbH, pages 171 and 201/202).
A significant disadvantage of filter press technique is that very high demands must be made of the edge seals of the fuel cell battery because the respective reaction agents, i.e. oxidant, fuel and coolant, must be reliably sealed from one another. Up to now, for example, an especially ticklish, direct sealing without buffer area that must assure that oxidant and fuel cannot overflow into one another is required at the edges of the bipolar plates. It is self-evident that such demands made of the edge seals are reflected in the manufacturing costs of the batteries. There is therefore a need to overcome the previously known filter press technique, not only given air-cooled fuel cells as in the above-cited German Letters Patent 44 42 285, but also given liquid-cooled fuel cell batteries.